Method and installation for treating a storage site

Abstract

The tank (1) is purged by gaseous nitrogen resulting from the vaporization of liquid nitrogen which has undergone an indirect heat exchange (2) with the gas issuing from the tank. This enables the purged products to be recovered. Application in the deballasting of ships transporting liquified petroleum gas or natural gas.

We claim: 
     
       1. A method for treating a storage site, and in particular for purging and rendering inert a tank, comprising minimizing the loss of time and maximizing the recovery of a gaseous product, otherwise resulting from conventional purging, by expelling a said gaseous product contained in said site by injecting nitrogen therein, effecting an indirect heat exchange between the gas issuing from said site and liquid nitrogen so as to partly condense said gas, and injecting into said site gaseous nitrogen resulting from said vaporization of liquid nitrogen. 
     
     
       2. A method according to claim 1, for purging and rendering inert a tank, comprising injecting said gaseous nitrogen into the tank at an opposite end of the tank to an outlet orifice for the gases of said tank. 
     
     
       3. A method according to claim 1, further comprising, in an advanced stage of the method, effecting a heat exchange between the gas issuing from said site and the gas resulting from said partial condensation, the latter gas being added to said gaseous nitrogen. 
     
     
       4. A method according to claim 1, comprising sending the gas resulting from said partial condensation into an upper part of a vessel storing the liquid recovered upon said condensation. 
     
     
       5. A method according to claim 1, comprising compressing the gas issuing from said site. 
     
     
       6. A method according to claim 5, for a storage site containing a gaseous product at low temperature, comprising effecting an indirect heat exchange between the gas issuing from said site and the compressed gas. 
     
     
       7. A method according to claim 1, comprising effecting an indirect heat exchange between the gas issuing from said site and the liquid resulting from said partial condensation. 
     
     
       8. A method according to claim 1, comprising, in an advanced stage of the method, completing said injection of gaseous nitrogen by an injection into said site of gaseous nitrogen coming from an exterior source. 
     
     
       9. An installation comprising: means for treating a storage site, and in particular for purging and rendering inert a tank, sufficient to minimize the loss of time and to maximize the recovery of a gaseous product, otherwise resulting from conventional purging, including a phase separator; a storage vessel communicating with the phase separator; and an indirect heat exchanger comprising first passageways for connection on the upstream side of the heat exchanger to said site and connection on the downstream side of the heat exchanger to the separator, and second passageways connected on the upstream side of the heat exchanger to a source of liquid nitrogen and for connection on the downstream side of the heat exchanger to said site. 
     
     
       10. An installation according to claim 9, for purging and rendering inert a tank, wherein said first and second passageways are adapted to be connected to orifices of the tank which are in opposed relation to each other. 
     
     
       11. An installation according to claim 9, comprising a compressor interposed between said site and an inlet of said first passageways of the heat exchanger. 
     
     
       12. An installation according to claim 11, comprising an auxiliary indirect heat exchanger including third passageways connected to a lower part of the phase separator and a lower part of the storage vessel, and fourth passageways for connection on the upstream side of the auxiliary heat exchanger to said site and for connection on the downstream side of the auxiliary heat exchanger to an inlet of said first passageways. 
     
     
       13. An installation according to claim 11, comprising an auxiliary indirect heat exchanger which puts in thermal exchange relation an inlet conduit and an outlet conduit of the compressor. 
     
     
       14. An installation according to claim 11, comprising an auxiliary indirect heat exchanger including third passageways connected to a lower part of the phase separator and a lower part of the storage vessel and fourth passageways for connection on the upstream side of the auxiliary heat exchanger to said site and for connection on the downstream side of the auxiliary heat exchanger to an inlet of said first passageways, and an auxiliary indirect heat exchanger which puts in thermal exchange relation an inlet conduit and an outlet conduit of the compressor. 
     
     
       15. An installation according to claim 9, comprising means for sending gas issuing from the separator into said second passageway. 
     
     
       16. An installation according to claim 9, comprising means for sending gas issuing from the separator into said storage vessel. 
     
     
       17. An installation according to claim 9, comprising means for sending gas issuing from the separator into said second passageways and into the storage vessel.